Broad-band end-fire television antenna



Dec. 17, 1957 J. SCHWARTZ ETAL ,3 7, 8

BROAD-BAND END-FIRE TELEVISION ANTENNA Filed Nov. 14, 1956 sSheets-Sheet 1 INVEN TOR. JEROME SCHWARTZ YUEN T. LO

Dec. 17, 1957 .1. SCHWARTZ ETAL BROAD-BAND END-FIRE TELEVISION ANTENNA 3Sheets-Sheet 2 Filed Nov. 14, 1956 INVENTOR. JEROME SCHWARTZ YUEN T. LOBY 3 i ATTORNEYS.

Dec. 17, 1957 J. SCHWARTZ ET AL 2,817,085

BROAD-BAND END-FIRE TELEVISION ANTENNA Filed Nov. 14, 1956 3Sheets-Sheet 3 N) A B R I 63 6 v l IW' I I W HHEnHE V HHEDT4 r230 r240r250 26C 270 5| L l l l l I INVENTOR. Z 2,.- 2 2 2 2 2 R %M% ESHWARTZ LV l I I BY 6 N 0%; 11E 11E u 112 ATTORNEYS.

United States Patent BROAD-BAND END-FIRE TELEVISIQN ANTENNA JeromeSchwartz, Ellenville, N. Y., and Yuen Tze Lo, Urbana, Ill., assignors toChannel Master Corporation, Ellenville, N. Y., a corporation of New YorkApplication November 14, 1956, Serial No. 622,073

26 t'llaims. (Cl. 343-814) such areas an antenna having considerablegain is required (gain being the antennas signal gathering abilitycompared to a standard dipole antenna). It is normally not sufficientthat an antenna in such. areas have a high gain for only a few of thechannels in the band which it is designed to cover. On the contrary, itis desired that,

an antenna for such an area have a high gain at each channel to bereceived and that the gain across the complete band or hands formed byall the various channels be substantially constant or fiat.

A further feature of increasing importance in television antennas is theso-called front-tol-back-ratio. High gain antennas are highly directive,so that signals from a particular direction are received with a gainmany times as great as the gain for signals from other directions fromthe antenna. The direction from which signals are best received isdesignated the front of the antenna. Most antennas are also somewhatsensitive in other directions and particularly to the direction oppositevto the front, namely the back of the antenna. In fact, for mostantennas, the second most sensitive direction is the back of theantenna, which in some cases may have a gain equal to the front gainunless special provision is made, as by use of a reflector.

As the number of television stations has increased and televisionstations have increased their power, the problem of interference'betweenstations has increased. Interference may occur between two televisionstations on the same channel or on adjacent channels. An interferingstation is seldom located in the same direction as the desired station,and thus an antenna with a high degree of directivity is very effectivein eliminating this interference except from the back direction. Thedegree of directivity of antennas as to the back direction is frequentlydefined in terms of relative sensitivity in the forward and reversedirections, called front-to-back ratio. An antenna with a highfront-to-back-ratio is therefore very desirable, particularly in fringeareas where problems of co-channel and adjacent channel interferencearise most often.

The basic type of antenna previously considered to be r most effectivein overcoming the problems described meat behind the active element. (Byin-line is meant in a common horizontal plane with elements spaced inthe front-to-back direction.)

In spite of its superiority in some respects over many other types ofantennas, the broad-band Yagi is still subject to many limitations. Abasic theoretical condition for maximum receiving antenna performance ina multielement antenna is that every element should produce an equalamount of current in the proper phase relationship. The broad-band Yagiantenna cannot fulfill this condition on more than one or twochannelsbecause the current and phase relationships do not hold constant acrossthe V. H. F. band. Since it cannot make full use of the transmittedenergy at all frequencies, this atnenna type cannot realize uniform gainon every channel and is not properly called broad-band.

The ability of the Yagi antenna to produce a high front-to-back-ratio onall channels is also inherently limited. The impedance of each parasiticelement and the physical spacing between them, determine both the phaseand the amplitude ofthe current flowing in the parasitic elements sinceno electrical connection is provided to them.

Ideally, automatic compensation should be provided to maintainsubstantially equal current in the proper phase for changes infrequency. However, the physical character of the parasitic element isfixed and therefore changes in current magnitude and phase mustinvariably occur with changes in frequency.

. Antennas according to the present invention are not subject to theinherent limitations of the broad bandYagi antenna due to the fact thatthe presentantenna does not rely on forward parasitic elements(directors) to increase the antenna gain. On the contrary, all theelements of the antenna are active with the exception of a single rearparasitic element (reflector). Since the forward elements of the antennaare all thus connected by an electrical transmisson line, the currentand phase relationships of each element are not determined solely by itsphysical dimensions but also by the current flowing in the transmissionline. -Proper design of the present antenna can therefore provide anantenna in which every element provides a substantially equal amount ofcurrent for all channels in the band.

It is accordingly an object of the present invention to provide atelevision antenna having multiple in.-line active elements wherein eachelement produces substantially an equal amount of current in the properphase relationship at every channel in the band.

It is a further object of the present invention to provide a televisionantenna having a number of in-line dipole elements wherein all of theelements except a reflector element are active elements connected to atransmission line.

It is still another object of the present invention to provide atelevision antenna having several in-line active dipole elements whereinthe impedances of the active elements are different, with the rearactive element having the .highest impedance and each successive elementin front of the rear element having a successively lower impedance withthis relationship maintained over the entire operating range.

It is still another object of the present invention to provide anantenna of the above type wherein the transmission line connecting theactive elements is of different characteristic impedance at differentpoints along its length to better balance the active elements ofdifferent impedance.

It is a further object of the present invention to provide a televisionantenna having several in-line active dipole elements of the V-typewherein the impedances of the activeelements are different, with "therear active element having the highest impedance and each successiveelement in front of the rear element having a successively lowerimpedance at all operating frequencies.

It is a further object of the present invention to provide a televisionantenna of the above type wherein the forward elements are constructedwith a smaller included V angle and the rear elements are constructedwith a larger V angle so that the currents in the elements aremaintained more nearly equal throughout the band and the proper phaserelationship is better maintained through-' out the band.

It is a still further object of the present invention to provide atelevision antenna having several in-line active elements with the rearactive element having the greatest impedance and the impedances of theremaining elements being graduated toward the front of the antenna atall operating frequencies, and further having a terminating resistor atthe forward end of the antenna for eliminating reflection and improvingthe front-to-backratio of the antenna.

It is a still further object of the present invention to provide atelevision antenna wherein all of the elements of the antenna arephysically folded elements in a vertical plane so that each of theelements is in eifect a trusslike member having a greater resistance todownward bending.

Further objects and advantages of the present invention will be apparentfrom a consideration of the following description in conjunction withthe appended drawings, in which:

Fig. 1 is a perspective downward view of a 7-element television antennaaccording to the present invention;

Fig. 2 is a perspective partly schematic view of a -element televisionantenna according to the present invention;

Fig. 3 is a perspective partly schematic view of a 3-element televisionantenna according to the present invention;

Fig. 4 is an enlarged fragmentary perspective view of the mountingstructure of the hairpin dipole elements of the antennas shown in Figs.1, 2 and 3;

Fig. 5 is an enlarged fragmentary perspective view showing the mountingstructure for the three-conductor dipole element of the antennas inFigs. 1, 2 and 3;

Fig. 6 is an enlarged fragmentary perspective view of the mountingstructure for the reflector element of the antennas in Figs. 1, 2 and 3;

Fig. 7 is an enlarged fragmentary perspective view of the U-bolt andcross-arm mounting clamps of the antennas of Figs. 1, 2 and 3;

Fig. 8 is a schematic diagram of a 7-element antenna according to thepresent invention useful in explaining the theory of operation of theantenna;

Fig. 9 is a schematic diagram of the hairpin-type dipoles used in thepresent invention;

Fig. 9a is a schematic diagram of a conventional folded dipole;

Fig. 10 is a schematic diagram of a V-type dipole antenna showing thecurrent distribution for the antenna;

Fig. 11 is a diagram of the current distribution in a circuit equivalentto the V-type dipole presented to demonstrate the theory of operation ofthe V-type dipole; Fig. 12 is a schematic circuit diagram of asubstantially equivalent electrical circuit for a 7-element antennaaccording to the present invention;

Fig. 13 is an impedance curve of a typical dipole antenna presented toaid in the explanation of the theory of operation of the presentantenna;

Figs. 14a, 14b and 140 are impedance curves of respective ones of thedipoles of an antenna according to the present invention presented toexplain the theory of operation of the antenna.

Referring now to Fig. 1 and to Fig. 7, a 7-element antenna according tothe present invention is shown at 11. The antenna 11 is supported by amast 12; a double secured to the cross-arm 16 of the antenna 11.

4 cross-boom 13 is connected to the mast 12 by means of a cross-armclamp 14 and U-bolts 15. The cross-boom 13 is constructed of a lowercross-arm 16 and a similar upper support-arm 17. The cross-arm 16 andthe support-arm 17 are rigidly secured together in spaced relationshipby a number of truss members 18.

The provision for two structural arm members, namely the cross-armmember 16 and the support-arm member 17 renders the structure of antennaunusually sturdy by utilizing the truss principle of construction.

The electrically operative portion of the antenna consists of sevenV-type reflector and dipole elements 21, 22, 23, 24, 25, 26 and 27. TheV-type reflector 21 is composed of two arms 21a and 21b located at anobtuse angle to one another and forming the arms of the V. The dipoleelements 22, 23, 24, 25, 26 and 27 are similarly composed of two arms22a and 22b, 23a and 23b, 24a and 24b, 25a and 25b, 26a and 26b, and 27aand 27b, respectively. Each of the arms of elements 21 and 23--27 isformed of a single conductor doubled back on itself to form a fold orhairpin.

The manner in which the antenna elements are secured and connected maybest be seen by reference to Figs. 4, 5 and 6. Each of the arms 21a and21b is secured to a respective mounting strap 31, and the mounting strap31 is further secured to a mounting block 41 The other pairs of arms aresimilarly secured to respective mounting blocks 42, 43, 44, 45, 4-6 and47 by means of respective mounting straps 32, 33, 34, 35, 36 and 37. Themounting blocks 4247 are formed of a dielectric insulating material. Thearms 21a and 21b, the straps 31 and the blocks 41 may be connectedtogether by riveting, bolting or any other suitable means. The mountingblock 41 is also connected to the cross-arm 16 by riveting, bolting orother suitable means. The

other elements 2227 are assembled and secured to the crossarm 16 in asimilar manner. The straps 3137 are of conductive material and serve thepurpose of providing an electrical connection to complete a closedelectrical loop for each of the dipole arms.

Dipoles 21 and 22 are provided with connecting bars 49 and 50respectively for electrically connecting the arms of the dipoles attheir centers. The bars 49 and 50 are fastened between straps 31 andbetween straps 32 respectively so that the reflector arms 21a and 21band the dipole arms 22a and 22b are each electrically connected at theircenters. The other five elements are center-fed hairpin dipoles and aretherefore not provided with connecting bars.

The dipole 22 dilfers from the other elements in that it is providedwith center conductors 28a and 23b. The center conductors 28a and 28bare conductively connected at their outer ends to the respective outerbends of the dipole arms 22:: and 22b. In addition a shorting bar 29a ofconductive material interconnects the two outer conductors of dipole arm22a and its center conductor 28a at a point near the end of the dipolearm 22a. A similar shorting bar 29b is similarly connected across thedipole arm 22b and the center conductor 28b. The inner ends of thecenter conductors 28a and 28b are not electrically connected to thestraps 32 as may be seen in Fig. 5. Electrical terminals 48 are providedat the inner ends of the center conductors 28a and 28b for connecting anelectrical transmission line 38 to the dipole 22. The significance ofthis particular construction of the dipole element 22 will be explainedin connection with the explanation of the electrical theory of operationof the antenna below.

The transmission line 38 provided for connecting the antenna 11 to atelevision receiver is connected to the antenna at terminals 48 of the3-conductor dipole 22. A second electrical transmission line section 230is elec trically connected between the terminals 48 of the 3- conductordipole 22 and respective straps 33 of the dipole element 23. A thirdtransmission line section 240 connects the straps 33 of the dipole 23 tothe straps 34 of the dipole 24. A transmission line section c similarlyconnects the dipole 24 to the dipole 25, another transmission linesection 260 connects the dipole 25 to the dipole 26, and still anothertransmission line section 27 connects the dipole 26 to the dipole 27 ina similar manner.

As seen in Fig. 1, 6 of the 7 elements of the antenna are connected bymeans of successive transmission line sections to the televisionreceiver. The transmission line harness sections 260 and 270 leading tothe front two dipoles 26 and 27 are preferably constructed with a widerconductor spacing and thus have a higher characteristic impedance thando other sections of the transmission line. Although this constructionutilizing diflerent types of transmission line is preferred, all thetransmission line sections may be made of the same type line.

As seen in Fig. 1, the front dipole 27 has arms 27a and 27b which areshorter than the arms of any of the other dipoles. The arms of thevarious dipole elements are progressively longer for dipoles 26, 25, 24and 23. This is a significant feature of the invention and will beexplained in detail in connection with the explanation of the theory ofoperation of the antenna.

In addition, the four front dipole elements 24, 25, 26 and 27 have asmaller V-angle than do the three rear elements 21, 22 and 23. Thisfeature further improves the operation of the antenna, as will beexplained below.

Fig. 2 shows an antenna 11a according to the present invention havingonly 5-elements rather than the 7-elements of the antenna shown in Fig.l. The antenna of Fig. 2 naturally has less gain than the more elaborateantenna of Fig. 1. However, in some instances a smaller amount of gainis required, and in the development of the very high-gain 7-elementantenna desirable attributes were developed which are also useful inantennas of lower gain.

In the S-element antenna 11a, the element 21 is a reflector element asbefore, the element 22 is a B-conductor folded dipole element as before,and the elements 23, 24 and 25 are center-fed hairpin dipoles, all as inantenna 11 of Fig. 1. The major change in the antenna 11a is theelimination of the front two elements of antenna 11, namely, the dipoles26 and 27. The V-angle of the dipoles 24 and 25 is somewhat less thanthe V-angle of the rear elements 21, 22, and 23 as was the case with the7-element antenna 11 in Fig. 1. The length of each of dipole elements23, 24 and 25 is successively less than that of the preceding one toprovide elements of diminishing impedance progressing toward the frontof the antenna. The transmission line sections between various antennaelements may be selected to have different impedances to improve theantenna characteristics. The dimensions and characteristics of aparticular preferred embodiment of the S-element antenna is provided inthe table below.

Fig. 3 shows a further simplified version of an antenna according to thepresent invention. A 3-element antenna 11b is shown having only areflector element 21, a 3- conductor folded dipole element 22 and ahairpin dipole element 23. The 3-element antenna 11b will, of course,have still less gain than the S-element antenna 11a. The antenna 11b istherefore particularly adapted for situations in which high gain is notrequired and where the broad-band, flat response and other desirablefeatures of the present antenna will be particularly useful.

Any of the present antennas and particularly the 7- element antenna maybe modified to have a higher frontto-back-ratio by providing aterminating resistor connected in parallel with the front element of theantenna. In

the 7-element antenna 11, for example, a terminating re-' point. Theterminating resistor may of course, be omitted, and it normally wouldnot be used with the 3-element and 5-element antennas which do notrequire as high front-to-back ratio in any case.

In view of the fact that the proper operation of any antenna depends tosome extent upon the physical dimensions and upon the electricalcharacteristics of its various elements, three particularly preferredrepresentative constructions for antennas according to the present 1Shorting bars 7% from ends of dipole arms.

Terminating resistor, if used, should preferably have a value ofapproximately 500 ohms.

Table Il.-5-element antenna impedspacing transmission lengthforward anceof from line length element center tilt of transadjacent from adjatotip, arms, mission element eentelement inches degrees line to (rear),(rear), element inches inches 1 Erefl.) 54 30 2 3-eonducto 1 50 30 3(hairpin) 52 30 4 (hairpin).. 48 40 5 (hairpin) 48 40 1 shorting bars 8%from ends of dipole arms.

Table III .-3-element antenna impedspacing transmission lengthforwardance of from line length element center tilt of transadjacent fromadjato tip, arms, mission element centelement inches degrees line to(rear), (rear), element inches inches 1 (mil) 54 30 2 (S-conductor) 1 4930 300 25 3 (hairpin) 50 40 425 20 24 1 Shorting bars 6% from ends ofdipole arms.

Tubing for antenna elements is preferably O. D. except for the centerconductor of the 3-conductor element which is O. D.

Distance between conductors of folded dipoles (outside conductors of3-conductor dipoles) is preferably 2%" center to center.

A theory of operation of the present antenna will now be explained byreference to Figs. 8 through 12. Fig. 8 shows schematically theapproximate equivalent electrical circuit of the 7-element antenna 11shown in Fig; 1. In Fig. 8 it may be seen that the reflector element 21is not electrically connected to the other antenna elements but has itsarms connected together. The element 22 is a 3-conductor folded dipolein which the center conductors are connected by means of a transmissionline to the other active antenna elements. The element 22 is the mainelement of the antenna, or in other words, the element connected by thetransmission line 38 to the television receiver. The antenna elements23, 24, 25, 26 and 27 are all hairpin dipole elements and are allelectrically connected by means of transmission line segments 230 to 270to the main element 22 and from there to the television receiver. Aterminating resistor 51 is connected across the terminals .of theforward antenna element'27.

As;:previously explained, the dipoles '23 to :27 in the preferredembodiments :of the .antenna are hairpin-type dipoles. The manner inwhich hairpin dipoles differ from ordinaryfolded dipoles is shown inFigs. '9 and 9a. As shown in Fig. 9 the hairpin dipole has bothconductors 52 .and, 53 of each arm-connected together at both ends, andconnected at the inner ends .to a'respective conductor of a transmission:line'54. On theother hand, as zShOWl'l in Fig. 9a, an ordinary foldeddipole has only one conductor 52 of each arm connected to a respectiveconductor of a transmissionline 54. The outer ends of conductors 52 ,arejoined by a separate single long conductor 55 parallel to conductors"52to form a single elongated loop from ,one terminal .of the line to theother. The hairpin conductor of Fig. 9 has more desirable impedancecharacteristics -in the present arrangement .and it is therefore.preferred that such .dipoles be utilized in the construction of thepresent antenna.

In explaining the operation of the antenna .it is desirable to firstexplain the operationpf a single oneof the V-dipole elements. It is animportant feature of the present invention, where the antenna is to beused as a dual-band V. H. F. television antenna, toqconstruct each ofthe dipole elements with its arms'tilted slightly 'forward toward thesource of received signals. V. H. F. television signals are broadcast intwo separate bands with channels 2 through 6 being in the lower bandbetween 54 and 88 megacycles per second and channels 7 through 13 in theupper hand between 174 and 216 megacycles per second. Approximately halfof the television channels therefore have frequencies which are roughlythree times the frequencies of the other half of .the televisionchannels. It has been found by early workers in the television antennaart that the frequency response curve of a dipole antenna for dual-bandV. H. F. television signals can be improved by tilting the arms of thedipole forward at an angleof 30 to 40 or so.

One general theoretical explanation of this phenomenon may be explainedby reference to Figs. 10 and 11. A dipole which is one-half wavelengthlong in the lower band will be three half-wavelengths long in the upperband. A dipole 56 is shown in Fig. 10 with dashed lines 57 indicatingcurrent distribution for low band signals and dotted lines 58 indicatingcurrent distribution for highband signals. In a straight dipoleanti-phase high band operation would result but in the V-dipole suchanti-phase high band operation is made harmless because the centersection of the V-antenna is located approximately 180 in space behindthe two outer sections. The approximate equivalent of this situation isshown in Fig. 11 where the outer dipole arm sections are shown at 59 andthe center section at 61. The current distribution of the outer sections59 is indicated generally by the solid lines 62. The currentdistribution of the central section 61 in absence of the space phasedifference is indicated by the dotted line 63. The space phasedifference of 180 converts the current distribution of 63 into thereverse distribution 64 so that the current of all three sections is inphase 7 and the eifect of anti-phase high band operation is avoided. TheV-dipole thus operates well on both low and high bands.

All of the dipole elements of the antenna are of the V-type and henceutilize the principles explained above. The V-type dipole cannot beadvantageously adapted for use with the Yagi antenna due to the factthat the inter-:

In order to explain the combined-operation of the mul tipleN-typehairpin dipoles. connected as shown in Fig. 8, 'it is useful toconsider'for amomenta circuit in which the-dipole elements are replacedbytheirrespective impedances at a given frequency. Such a circuit isshown in Fig. 12 where the various antenna elements equivalentimpedances are represented schematically. The impedanceiof the reflectorelement .21 is represented atZ and it may be-noted thatthe reflectorelement is not physically connected in the :transmission line circuit.The three-conductor dipole 22 isrepresented by the impedance Z Theimpedances of the remaining dipole elements are represented by theimpedances'Z Z Z Z and Z The terminating resistor 51 is shown connectedacross the terminals-of the impedance Z The basic directivity-pat-terns(and thus the gain) of an antenna are determined by the phases andamplitudes of the currents in the dipoles of the antenna as well as bythe position of the dipoles in respect to each other. It has previouslybeen explained that the current in each of the active dipoles of thepresent antenna is controlled in part by the current flowing in thetransmission line sections between theelements of the antenna.

As seen in Figs. 1, 2 and 3, and described above, the transmission lineharness length between each pair of adjacent dipoles-is greater than thefree space distance between the same two dipoles which increases thedirectivity over a conventional end-fire antenna.

For maximum antenna performance each dipole of the antenna should alsohave an equal amount of current induced in it. It is therefore desirableto select the impedances shown in Fig. 12 so that this result isobtained. It would at first appear that the current in each of theimpedances shown in "Fig. 12 (that-is, in Z Z Z Z Z and Z would be equalif each of the foregoing impedances were equal. This is'notthe case,however, due to the fact that the signalsinvolved have wavelengths notsubstantially different from the'spacings-of the antenna elements, andthus low-frequency alternating current theory is not applicable.

The proper selection of the impedances in Fig. 12 may be understood 'byutilizing the concept of reciprocity and considering the 7-elementantenna in question as a transmitting antenna for the moment.Considering the antenna ,as a transmitting antenna, the feed elementimpedance Z should be relatively large so that the major portion of thesignal sent into the antenna will not be absorbed and transmitted by thefirst or feed element Z It is rather desired that only approximatelyone-sixth of an input signal be absorbed or radiated by the impedance Zand that the remainder be transmitted about the transmission line. Asthe signal continues down the harness 23c it is desired that a greaterportion, namely, about one-fifth of the remaining signal be absorbed bythe impedance Z Therefore, in order to accomplish the desired result,the impedance Z should be less than the impedance Z At the impedance 2it is desired that approximately one-fourth of the remaining signal bediverted, and so on to the end of the transmission line, so that eachimpedance Z through Z will have received substantially an equal currentfrom the transmission line.

It is impracticable, of course, to arrange that all of the remainingsignals be absorbed by the last impedance Z and thus the terminatingresistor 51 may be provided to absorb substantially all of the remainingsignal and prevent reflections from the end of the transmission lineharness which would tend to cause undesirable back-lobes in the antennapattern which would impair the desired high front-to-back-ratio.

Correlating the principles explained in, connection with Fig. 12 with,the physical construction of theantennaschematically represented inFig. 8, .themain dipole 22 is a three-conductor dipole and thus hasasubstantially higher impedance than .does a hairpin dipole ,of the samelength. Although the three-conductor dipole 22 is, physicallysomeshims-'5 what shorter than the longest hairpin dipole 23, thethreeconductor dipole 22 has the highest impedance of any of the activedipole elements of the antenna. The rear active hairpin dipole 23 is thelongest of any of the hairpin dipole elements and thus has the greatestimpedance among them. Each of the dipoles 24, 25, 26 and 27 issuccessively shorter than its preceding dipole, and hence each hassomewhat lower impedance than the dipole immediately to its rear.

Therefore, by comparing the physical structure of the antenna with thetheoretical optimum situation explained with reference to Fig. 12, itwill be seen that the present antenna is constructed to create acondition where each dipole receives substantially the same current andthus substantially optimum antenna performance may be realized. Althoughthe principle of operation has been explalned in terms of transmission,it will be understood that an antenna designed for maximum transmissionefliciency will likewise provide maximum reception efficiency inaccordance with the principle of reciprocity in antenna design.

It is not sufficient for the equal current conditions discussed above toexist only for a limited frequency range within the frequency bandsought to be recovered. Other antennas are able to realize theseconditions for limited frequency ranges. The most outstanding advantageof the present antenna resides in the fact that it can maintainsubstantially equal current in the antenna elements throughout asubstantial range of frequencies such as over both the V. H. F.television bands. The manner in which these conditions are thusmaintained is explained by reference to Figs. 13 and 14.

Referring first to Fig. 13, there is shown a typical spiral curve of theimpedance of a dipole. The line OR represents resistances from zerotoward infinity. Inductive reactances X are indicated by distances abovethe line OR. Capacitive reactances X; are indicated by dis 'tances belowthe line OR.

It will be observed that the impedance spiral crosses the horizontalline OR at a number of points A, B, C and D and thus the impedances atthe given points are effectively resistive and the dipole is resonant.

It may be assumed that the points A, B, C, and D represent the first,second, third and fourth harmonics or in other words, points where adipole is /2, 1, 1 /2 and 2 wave-lengths long. It will be seen that thedipole characteristics are about the same between points A and B betweenpoints C and D; that is, the total impedance (which is the distance froma point in the curve to point diminishes as frequency is decreased, fromB to A or D to C. The present antenna takes advantage of this fact inorder to provide superior performance over both the low V. H. F. bandand the high V. H. F. band, where the two bands have a frequency ratioof approximately 3 to 1.

As previously indicated it is necessary that the decreasing relationshipof the impedances of the successive antenna elements must be maintainedfor all frequencies in the band to be covered. The manner in which thepresent antenna construction accomplishes this will be understood byreference to Figs. 14a, 14b and 140 which show impedance diagrams withreference to a S-element antenna, but the same principle would apply toantennas having a greater or lesser number of elements. The feed element22 represented by the impedance Z is constructed as a threeconductordipole to assure that the feed element 22 will always have a higherimpedance than any of the other antenna elements. The particularimpedances desired for the three-conductor dipole is attained bysuitably positioning the shorting bar 2% across the three-conductordipole.

The remaining problem then is to assure that the proper impedancerelationships are maintained in the three reinaining hairpin dipoles,and it is the solution to this problem which is explained by referenceto Figs. 14a, 14b. and 14c. Fig. 14a represents the impedance spiral ofthe first hairpindipo'le 23., Fig. 14b represents the,impedance spiralof the second hairpin dipole 24. Fig. 14 represents the impedance spiralof a third or front harpin dipole 25. In Fig. 14a, four points arerepresented having reference numerals 2, 6, 7 and 13. These numeralscorrespond to channel numbers in the V. H. F. television band, channels2 and 6 being respectively the lowest and highest frequency channels inthe low V. H. F. television band, and channels 7 and 13 beingrespectively the lowest and high est frequency channels in the upper V.H. F. band.

As seen in Fig. 14a the first hairpin dipole element has a length suchthat a maximum resonant impedance for the element results at a frequencyapproximately corresponding to channel 6 of the V. H. F. televisionband. This element is thus cut to channel 6. The impedance for lowerfrequency channel-2 signals is less than that for channel-6 signals, butthe impedance for channel-2 signals is more than the impedance minimumcorresponding to point A in Fig. 13. The physical configuration of thedipole is such that the channel-13 and of the channel-7 points fall inpositions on the inner loop of the impedance spiral generallycorresponding to the location of the channel-6 point and the channel-2point on the outer loop of the impedance spiral.

The second driven hairpin dipole 24 has a physical length somewhatshorter than that of the dipole 23 and the impedance spiral of thatdipole is represented in Fig. 14b. Since the dipole 24 has a lengthwhich is a somewhat smaller fraction of a wavelength than was the dipole23, the channel-6 point is moved clockwise around the impedance spiralrelative to its location in Fig. 14a. All the other impedance points forthe other channels are moved a corresponding distance around the spiralin a counter clockwise direction. In Fig. the impedance spiral of thestill shorter element 25 is shown and thus the impedance points for thevarious corresponding channels are moved still farther in acounterclockwise direction around the impedance spiral of Fig. 140.

By comparing the relative location of the channel-6 impedance points inFigs. 14a, 14b and 140, it will be observed that the impedance of thesecond hairpin dipole as shown in Fig. 14b is less than that of thefirst hairpin dipole shown in Fig. 14a for channel-6 frequencies. Theimpedance at channel-6 frequencies of the third hairpin dipole as shownin Fig. 140 is still less than that for the preceding dipoles.

Comparing the impedances of each of the three dipoles at frequenciescorresponding to other V. H. F. television channels, it will be seenthat regardless of the received frequency (within the V. H. F.television bands) the impedance of the dipole 24 for that particularfrequency is less than the impedance of the dipole 23 and the impedanceof the dipole 25 is still less than that of the dipole 24. Therefore thepresent antenna construction utilizes these various principles toachieve an antenna construction wherein the current received in each ofthe television antenna elements tends to be substantially equal not onlyfor a portion of the V. H. F. television band, but for each channel inboth the upper and lower V. H. F. television bands. The present antennatherefore achieves a result which was impossible of accomplishment withprevious high-gain antennas such as the Yagi and its variations.

The invention is not limited to the particular means for providingelements of progressively diminishing impedance described above. Inaddition to varying the length and configuration of the antenna elementsin the manner described, other schemes for providing elements ofdifferent impedances might be used. The invention is not limited to theuse of particular types or numbers of dipole or other elements for theantenna. However; the three-conductor folded dipole 22 with shortingbars 29a, 29b is particularly adapted for use with the present antenna.The three-conductor dipole is a high impedance element and. byincorporating shortinghars. which :may be located at various points;near the ends of the dipole, an :antenna element ;of relatively high,adjustable impedance is provided. The shortingbar for the threeconductorqdipole is located at slightly different positions in the 3-, 5- and7-element antennas in order to provide slightly different impedances forthe element and thereby obtain optimum antenna characteristics in therespective antenna configurations.

It will alsoibe observed that the use of doubleor triplerod construction;.for all antenna elements provides an antenna structure of.superior'physical strength.

The particular'embodiments of the antenna described above .are designedto operatefinconjunction with a300- ohm transmission line to thetelevision receiver. Antennas utilizing the same-principle -may ofcourse be-designed to have'a lower or'higher impedance suitable for usein conjunction with transmissionlines of lower or higher impedances.

vIn the foregoing .explanation it was shown .that the characteristics ofthe antenna could be improved by utilizing transmission line harness ofdifferent characteristic impedances for connecting certain of theantenna elements. Table I, for example, shows that a preferredembodiment of the 7-element antenna utilizes 300-ohm transmission linefor the main'transmission line harness sections to the third, fourth andfifth elements of the antenna. The sixth and seventh elements at thefront antenna are connected, however, by means of higher impedancetransmissionline, ,for example of 425-ohms. By utilizing a highimpedance harnessfor-the front two antenna elements, these elementsabsorb the proper amount of.power so that the equalized power absorptionpreviously explainedis attained.

As also described above, the front elements in the preferred embodimentsof thepresent antenna are tilted forward at a sharper angle. Thisfeature, though not essential for the practice of the invention, doeshowever produce further improvements in the antennacharacteristics.Rather than using the two particular angles of 30 and 40 as described inthe preferred embodiments above, theantenna elements couldbe set at morethan two different angles, differing more or lesszfrom 30 and 40. Theimportant characteristic of the tilt angles of the antenna elements isthat at least one ,of the forward elements be tilted forward at asharperangle than other elements to the rear of the forward element orelements. It is thought thatthe improvement brought about by thedifference intilt anglesis due to rather, complex interaction betweenthe'forward .and rear antenna elements. No entirely satisfactorytheoretical basis for the improved characteristics afforded by thisconstruction is available.

Although preferred embodiments of antennas according to the presentinvention have been shown and described in great detail, it should beunderstood that the invention is not limited .to thedetails described.For example, the specific manner in which the antenna elements aresupported in position is obviously not important with respect to theirelectrical functioning. It is also obvious to those having a knowledgeof the antenna art that other types of dipole antenna elements could besubstituted for the particular type of elements shown in the preferredembodiment of the present invention. The presentinvention could bepracticed with a greater or lesser degree of success with any of theseother type of antenna elements by selecting active elements constructedto have progressively increasing impedances as you approachthe rearactive element.

It is equally obvious that although the reflector element '21 in thevarious preferred embodiments of the present antenna is a hairpin dipoletype reflector element, other equivalontreflector elements, dipole orotherwise,

-could=also-be used in an antenna according to the present invention.

The particular embodimentsof the antenna described were designed for useas television receiving antennas 12 primarily. The invention'is notlimited to antennas for such use, however, and may be used for otherpurposes including transmission as well as reception.

While the theory of operation of the present antenna has been explainedin accordance with the best knowledge available, and the foregoingtheory of operation is believed to be correct, the present invention isnot to be limited by the theory of operation advanced above.

Thus an antenna is provided according to the present invention whichpossesses high gain and high front-toback-ratio as well as otherdesirable characteristics which are exhibited throughout a wide-band offrequencies such as the V. H. F. television band.

Although particular preferred embodiments of the present invention havebeen described in detail it will be .understood that many modificationscould be made by those skilled in the art within the scope of thepresent invention, and accordingly the present invention is not to belimited by the particular embodiment shown and described. Rather thepresent invention is to be limited solely by the appended claims.

What is claimed is:

l. A broad-band directive antenna array comprising a plurality ofV-shaped dipole elements arrayed in file in horizontally spaced relationwith corresponding arms of said dipole elements disposed in a commonplane, the included V-angle of at least one of said V-shaped dipoleelements being less than that of others of said elements, said dipoleelements having progressively increasing impedance from front to back ofsaid antenna array at all frequencies in the operating band, signaltransmission means connected to at least two of said dipole elements toreceive a signal therefrom and a parasitic reflector antenna elementhorizontally displaced from an end one of said dipole elements.

2. A broad-band directive anenna array comprising a plurality ofV-shaped dipole elements arrayed in file in horizontally spaced relationwith corresponding arms of said dipole elements disposed in a commonplane, the included V-angle of at least one of said V-shaped dipoleelements being less than that of others of said elements, said dipoleelements having progressively increasing impedance from front to back ofsaid antenna array at all frequencies in the operating band, signaltransmission means connected to at least two of said dipole elements toreceive the signal therefrom and a parasitic reflector antenna elementhorizontally displaced from an end one of said dipole elements, saidreflector element having arms respectively parallel to the arms of saidend dipole element.

3. A broad-band directive antenna array comprising a plurality ofV-shaped dipole elements arrayed in file i'n horizontally spacedrelation with corresponding arms of said dipole elements disposed in acommon plane, the included V-angle of at least one of said V-shapeddipole elements being less than that of others of said elements, saiddipole elements having progressively increasing impedance from front toback of said antenna array at all frequencies in the operating band,signal transmission means connected to at least two of said dipoleelements to receive signals therefrom, said signal transmission meanscomprising a transmission line connected to a first of said dipoleelements and a further transmission line section connecting at least oneother of said dipole elements to said first of said dipole elements,said further transmission line section between said elements having alength greater than the physical spacing between said elements, and aparasitic reflector antenna element horizontally displaced from an endone of said dipole elements.

4. A broad-band directive antenna array comprising a plurality ofV-shaped dipole elements arrayed in file in horizontally spaced relationwith corresponding arms in said dipole elements disposed in a commonplane, the included V-angle of at least one of said V-shaped dipoleelements being less than that of others of said elements, and at leastone of said elements .being a high impedance senses type dipole having ahigher resonance impedance than others of said dipol 'elements and saidother dipoles havmg progressively varying impedance from front to backofsaid antenna at all operating frequencies, signal transmission meansconnected to at least two of said dipole elements to receive a signaltherefrom, and a parasitic reflector antenna element horizontallydisplaced from an end one of said dipole elements.

5. A broad-band directive television antenna array for both the high andlow frequency portions of the V. H. F. television band comprising aplurality of V-shaped dipole elements arrayed in file in horizontallyspaced relation with corresponding arms of said dipole elements disposedin a common plane, the impedances of said dipole elements beingdifferent at each antenna frequency within said V. H. F. television bandand arranged with increasing element impedance from the front to therear of the antenna for all frequencies in both said portions.

6. An antenna array as claimed in claim wherein the impedance of each ofsaid dipole elements is selected to maintain substantially equal signalcurrents in said elements.

7. A broad-band directive antenna array comprising at least threecoplanar V-shaped dipole elements arranged in substantially parallelspaced relationship with the bisectors of the V-angles of said elementscolinear and the vertex of the V of each element pointed toward the rearof said antenna, a parasitic reflector element in spaced relation withand to the rear of the rear one of said dipole elements, a firsttransmission line connected to the rear one of said dipole elements, andfurther transmission line sections electrically connecting each of saiddipole elements to the dipole element to its rear, said furthertransmission line sections between said elements having lengthsrespectively greater than the corresponding physical spacings betweensaid elements, said dipole elements having progressively increasingimpedance from front to back of said antenna array at all frequencies inthe operating band.

8. An antenna array as claimed in claim 7 wherein at least one of saidfurther transmission line sections has a characteristic impedancedifferent from said transmission line characteristic impedance.

9. An antenna array as claimed in claim 7 wherein at least one of therear-most ones of said dipole elements is constructed with an includedV-angle greater than the included V-angle of the front one of saiddipole elements.

10. An antenna array as claimed in claim 7 further including aterminating resistance element electrically connected between theterminals of the front one of said dipole elements.

11. A broad-band directive antenna array comprising a plurality ofdipole elements, each element comprising a pair of outwardly extendingarms each formed of elongated loops of conductive material, the loops ofeach pair of arms being relatively disposed at an angle to provide aV-shaped dipole element, said V-shaped dipole elements being arranged insubstantially spaced coplanar relation with the bisectors of theV-angles thereof in colinear relation and with the vertex of the V ofeach element pointed toward the rear of said antenna array, said dipoleelements further having different impedances at all frequencies in theoperating band and being arranged in order of increasing impedancetoward the rear of said antenna array for all said frequencies, aparasitic reflector element having a pair of extending arms formed ofelongated loops of conductive material, said loops being electricallyconnected at their inner ends and disposed at an angle to provide aV-shaped reflector element, said reflector element being disposed incoplanar parallel spaced relation with, and to the rear of, the rear oneof said dipole elements, a first transmission line connected to the rearone of said dipole elements, and further transmission line sectionselectrically connecting each of said dipole elements to the dipoleelement to its immediate rear, said further transmission line sectionsbetween said elements l4 having respectivelengths greater than thecorresponding physical spacings between said elements. a 12. Abroad-band directive antenna array comprising a plurality of dipoleelements, each element comprising a pair of outwardly extending armseach formed of elongated loops of conductive material, the loops of eachpair of arms being relatively disposed at an angle to provide a V-shapeddipole element, said V-shaped dipole elements being arranged insubstantially spaced coplanar relation with the bisectors of theV-angles thereof in colinear relation and with the vertex of the V ofeach element pointed toward the rear of said antenna array, said dipoleelements further having different impedances at all frequencies in theoperating band and being arranged in order of increasing impedancetoward the rear of said antenna array for all said frequencies, aparasitic reflector element having a pair of extending arms formed ofelongated loops of conductive material, said loops being electricallyconnected at their inner ends and disposed at an angle to provide aV-shaped reflector element, said reflector element being disposed incoplanar parallel. spaced relation with, and to the rear of, the rearone of said dipole elements, a first transmission line connected to therear one of said dipole elements, and further transmission line sectionselectrically connecting each of said dipole elements to the dipoleelement to its immediate rear, said further transmission line sectionsbetween said elements having respective lengths greater than thecorresponding physical spacings between said elements, the rear one ofsaid dipole elements having its elongated loops conductively connectedtogether at their inner ends and further including a conductor rod foreach of its arms extending substantially the length of the arm adjacentits corresponding elongated loops and conductively con-v nected near theouter end to said corresponding elongated loop and electricallyconnected near the inner end to a correspondingterminal of saidtransmission line.

13. An antenna array as claimed in claim 12 wherein at least the one ofsaid further transmission line sections connected to the front one ofsaid dipole elements has a characteristic impedance higher than thecharacteristic impedance of said first transmission line.

14. An antenna array as claimed in claim 11 wherein at least one of therear ones of said dipole elements is constructed with an includedV-angle greater than the included V-angle of the front one of saiddipole elements.

15. An antenna array as claimed in claim 11 further including aterminating resistance element electrically connected between theterminals of the front one of said dipole elements.

16. A broad-band directive antenna array comprising a plurality ofdipole elements, each element comprising outwardly extending arms formedof elongated loops of conductive material disposed at an angle toprovide a V-shaped dipole element, said dipole elements being arrangedin coplanar spaced relation with the bisectors of the V-angles thereofcolinear, with the vertex of the V of each element pointed toward therear of said antenna array, the included V-angle of at least the frontone of said elements being less than the included V-angle of the rearone of said antenna elements, said dipole elements further havingdifferent impedances at all frequencies in the operating band and beingarranged in order of increasing impedance toward the rear of saidantenna array for all said frequencies, a reflector element havingextending arms formed of elongated loops of conductive material, saidloops being electrically connected at their inner ends and disposed atan angle to provide a V-shaped reflector element, said reflector elementbeing disposed in spaced relation with, and to the rear of, the rear one.of

said dipole elements, a first transmission line connected to the rearone of said dipole elements'for coupling to othe apparatus, furthertransmission line sections elec-.- trically inter-connecting each pairof adjacent dipole: elements to complete an electrical path from each ofsaid dipole elements to said first transmission line, said furthertransmission line sections between said elements having respectivelengths greater than the corresponding physical spacings between saidelements, and at least the front one of said transmission line sectionshaving a higher characteristic impedance than that of said firsttransmission line, and a terminating resistor electrically connectedbetween the terminals of the front one of said dipole elements.

17. A broad-band directive television antenna array for both the highand low frequency portions of the V. H. F. television band comprising aplurality of V-shaped dipole elements arrayed in file in horizontallyspaced relation with corresponding arms of said dipole elements disposedin a common plane, the included V-angle of at least one of the rearrnostones of said dipole elements being greater than the included V-angle ofthe front one of said dipole elements, the impedances of said dipoleelements being different and arranged with increasing impedance from thefront to the rear of the antenna at all antenna frequencies within saidV. H. F. television band.

18. A broad-band directive antenna array comprising at least threecoplanar V-shaped dipole elements arranged in spaced relationship withthe bisectors of the V-angle of said elements colinear and vertex of theV of each element pointed toward the rear of said antenna, at least oneof the rearrnost ones of said dipole elements having an included V-anglegreater than the included V-angle of the front one of said dipoleelements, sai-d dipole elements having progressively increasingimpedance from front to back of said antenna array at all frequencies inthe operating band, a parasitic reflector element in spaced relationwith and to the rear of the rear one of said dipole elements, a firsttransmission line connected to the rear one of said dipole elements, andfurther transmission line sections electrically connecting each of theothers of said dipole elements to the dipole element to its rear, saidfurther transmission line sections having lengths between said elementsrespectively greater than the corresponding physical spacings betweensaid elements.

19. A broad-band antenna array for operation in a given frequency bandcomprising a plurality of active elements arrayed in file inhorizontally spaced coplanar relation, said active antenna elementshaving different impedances at every antenna frequency in said band andbeing arranged in order of increasing impedance toward the rear of saidantenna array for every frequency in said band, the impedances of saidactive antenna elements being further selected to maintain substantiallyequal signal currents in said elements throughout the antenna frequencyband, a reflector element horizontally displaced to the rear of the rearone of said active antenna element, and signal transmission meanselectrically connected to at least two of said dipole elements forcoupling said array to other apparatus.

20. A broad-band antenna array comprising a plurality of active elementsarrayed in file in horizontally spaced coplanar relation, said activeantenna elements having different impedances at all operatingfrequencies and be ing arranged in order of increasing impedance towardthe rear of said antenna array for all said frequencies; the impedancesof said active antenna elements being further selected to maintainsubstantially equal signal currents in said elements throughout theantenna frequency band, a reflector elem ent. horizontally displaced tothe rear ofthe rear one of said active antenna elements, signaltransmission means electrically connected to at least two of said dipoleelements for coupling said array to other apparatus, said signaltransmission means comprising a first transmission line connected toafirst of said antenna elements and a farther transmission line sectionconnected to at least one other of said active elements; said furthertransmission linesection havinga length between said elements greaterthan the physical spacing between said active elements, and said furthertransmission line section- 16, having a characteristic impedance higherthan the characteristic impedance of said first transmission line.

21. A broad-band directive antenna array comprising at least threecoplanar V-shaped dipole elements arranged in spaced relationship withthe bisectors of the V-angle of said elements colinear and the vertex ofthe V of each element pointed toward the rear of said antenna, at leastone of the rearrnost ones of said dipole elements having an includedV-angle greater than the included V-angle of the front one of saiddipole elements said dipole elements having progressively increasingimpedance from front to back of said antenna array at all frequencies inthe operating band, a parasitic reflector element in spaced relationwithand to the rear of the rear one of said dipole elements, a firsttransmission line connected to the rear one of said dipole elements, andfurther transmission line sections electrically connecting each of saiddipole elements to the dipole element to its rear, said furthertransmission line sections between said elements having lengthsrespectively greater than the corresponding physical spacings betweensaid dipole elements and at least one of said further transmission linesections having a characteristic impedance different from saidtransmission line characteristic impedance.

22. A broad-line directive antenna array comprising a plurality ofdipole elements, each element comprising a pair of outwardly extendingarms each formed of an elongated loop of conductive material with saidarms being disposed at an angle to provide a V-shaped dipole element,said dipole elements being arranged in coplanar spaced relation with thebisectors of the V-angles thereof colinear and with the vertex of the Vof each element pointed toward the rear of said antenna array, theincluded V-angle of at least the front one of said elements being lessthan the included V-angle of the rear one of said elements, said dipoleelements further having different impedances at all operatingfrequencies and being arranged in order of increasing impedance towardthe rear of said antenna array at all said frequencies, a reflectorelement having a pair of extending arms each formed of an elongated loopof conductive material electrically connected at their inner ends andsaid arms being disposed at an angle to provide a V-shaped reflectorelement, said reflector element being disposed in spaced relation with,and to the rear of, the rear one of said dipole elements, a firsttransmission line connected to the rear one of said dipole elements forcoupling to other apparatus, further transmission line sectionselectrically interconnecting each pair of adjacent dipole elements tocomplete an electrical path from each of said dipole elements to saidfirst transmission line, said further transmission line sections betweensaid elements having respective lengths greater than the correspondingphysical spacings between said elements.

23. A multi-band antenna for a high frequency band and a low frequencyband, the frequencies of said high frequency band being approximatelytriple the frequencies of said low frequency band, comprising aplurality of active dipole elements arranged in line, each of saidelements having respective half-wavelength, full-wavelength,three-halves wavelength and two-wavelength resonant frequencies, saidlow frequency band being between said half-wavelength and fullwavelength resonant frequencies of all said elements, and said high.frequency band being entirely betweenv said three-halves wavelength andtwowavelength resonant frequencies,sand said elements being arranged indescending order of resonant frequency from front to back of saidantenna, whereby said elements offer progressively increasing impedancefrom front to back of said antenna at all frequencies of said low andhigh bands.

24. An antenna as in claim 23 further including an additional activedipole element in back of said plurality of elements and having a higherimpedance than all said plurality of elements for all frequencies inboth said bands.

25. A wide-band antenna for operation over a given band of frequenciescomprising a plurality of active dipole elements arranged in line, allof said elements having resonant frequencies at or outside the extremeedge of said given band, and said resonant frequencies beingprogressively smaller from front to back of said antenna, whereby saidelements otter progressively increasing impedances from front to back atall frequencies of said given band.

26. A wide-band antenna for operation over a given band of frequenciescomprising a pair of active dipole elements arranged in line and spacedfrom the front to back of said antenna, said elements both havingresonant frequencies at or outside the extreme edge of said given band,the resonant frequency of said front element being References Cited inthe file of this patent UNITED STATES PATENTS 2,081,162 Alford May 25,1937 2,471,256 Wintermute May 24, 1949 2,772,413 Guernsey et a1 Nov. 27,1956

